Changing Planet: Ocean Acidification - The Chemistry is
Less than Basic!

Background

The
ocean-atmosphere interface is one place where exchanges take place all the
time. What if we change the balance of what is exchanged? For example, what if
we increase the amount of carbon dioxide in the atmosphere – will it impact the
amount of carbon dioxide that makes its way into our oceans? What will happen
to the chemical balance of ocean water and the marine life living there? In
this investigation, you will explore this exchange of gases and identify the
changes in the chemical balance of seawater.

Lab Question

How does the presence of
carbon dioxide change the pH of water? How has the increase in atmospheric carbon
dioxide changed the chemistry of our oceans?

Materials per lab team

Test tube rack

Five test tubes

One hole stopper with
tubing attached

Baking soda

Vinegar

Aluminum foil

Cotton balls

Bottle of BTB indicator solution

Straws

Sprig of Elodea

Masking tape

Markers

Distilled Water

250 mL beaker or plastic
cup

Graduated cylinder

Coral and shell specimens

pH indicator solution

Procedure

Part 1: Detecting CO2
Gas

With masking tape, label 4
test tubes A thru D. One test tube will be left unmarked. Bromothymol Blue
solution (BTB) is green if the solution is neutral, blue if it is a base
(alkaline), or yellow if it is an acid.

Fill test tubes A and B
approximately 1/3 full with the BTB solution and place in the rack. Test
tube A will be used as a control.

Fill the unmarked test tube
approximately 1/4 full of vinegar.

Using the foil, make a
small "boat" for the baking soda - fill 1/2 full of baking soda.
See Figure 1.

Figure 1

The 'boat' should be small
enough to easily fit into the test tube and float on the vinegar.

Carefully slide the foil
boat inside the unlabeled vinegar test tube (it is useful to tilt the tube
at an angle to accomplish this).

Plug the tube with the
stopper and tubing.

Place the free end of the
tubing in test tube B with BTB, making sure the end of the tubing reaches
the bottom of the tube. See Figure 2.

Figure 2

Place a cotton ball into
the neck of the tube with BTB.

Mix the vinegar and soda
together by GENTLY swirling the tube from side-to-side. Don't shake it
upside down! Gas bubbles will begin to bubble rapidly out of the tubing
into the test tube with BTB. See Figure 3.

Figure 3

Note the color change. What
happened? Record your observations in the Data Table 1.

Part 2: Are animals a source of CO2?

Fill a test tube C approximately
1/3 full of BTB

Place a straw in the test
tube.

Place a cotton ball in the
test tube opening.

Gently blow in the straw.

Note the color change. What
happened? Record your observations in the Data Table 1.

Part 3: Are plants a source of CO2?

Fill test tube D
approximately 1/3 full of BTB.

Place a sprig of Elodea
into the test tube (Use a pencil or pen to push it all the way into the
bottom of the tube.).

Wrap the tube in foil so
that no light can get in.

Place in test tube rack and
leave for at least 24 hours. (Your teacher has begun this part of the lab
up to this point.)

Unwrap the foil and note
the color change. What happened? Record your observations in the Data
Table 1.

Part 4: Do Plants take up CO2?

Using the now-unwrapped
test tube with Elodea from Part 3, leave in the light and observe the BTB
color change.

Note the color change. What
happened? Record your observations in the Data Table 1.

Part
5: Are Fossil Fuels a Source of CO2?

Your teacher will do this
for you as a demonstration.

Note the color change. What
happened? Record your observations in the Data Table 1.

Data Table 1:

BTB Color Change

Acid or Base

What Happened?

Part 1

From:

To:

Part 2

From:

To:

Part 3

From:

To:

Part 4

From:

To:

Part 5

From:

To:

Part 6: pH and Marine
Ecosystems

Gather the distilled water,
beaker/cup, straw, and pH indicator solution. Pour approximately 50 mL of
distilled water into the beaker/cup and add 15 drops of pH indicator
solution and swirl to mix the solution. Record the color of the solution
and pH in Data Table 2.

Using the straw, gently
exhale into the solution until you notice a color change in the solution.
Record the color of the solution and pH in Data Table 2.

Now add some crushed shells
or coral to your solution and swirl it around until the coral changes.
Record the color of the solution and pH in Data Table 2.

Date Table 2:

Color

pH

What Happened?

pH indicator solution +
water

***Initial color***

pH indicator solution +
water + breath

pH indicator solution +
water + breath + shells/coral

Analysis

1.
After finishing all the parts of this activity, compare the colors in all the
tubes. Are they different? Describe the phenomena that took place in each test
tube and the beaker/cup.

What happened to the
shells or coral after they remained in the solution for a little while?

Based on what happened in
this investigation, can the same effects happen in our oceans to marine
life with shells or calcium carbonate exoskeletons? Explain your answer.

Conclusion

1.
Use this image of the carbon cycle and the terms sources and sinks
to write a paragraph about the processes in the carbon cycle.

Figure 4: This
carbon cycle diagram shows the storage and annual exchange of carbon between
the atmosphere, hydrosphere and geosphere in gigatons - or billions of tons -
of Carbon (GtC).(Source:Wikipedia
Commons)

2.
What is meant by the term ocean acidification?

3.
When ocean acidification occurs, calcium carbonate molecules dissociate causing
a loss in shells, exoskeletons, or coral reefs. Research a marine organism
(other than coral) which relies on calcium carbonate for its exoskeleton. Use
the results of this lab to predict what would happen if our oceans became more
acidic.